34 Mr M. G. Potter, On the Structure of the Ice Plant. [Nov. 12, 



section through the base of a vesicle situated on the stem, and in 

 Fig. VIII. a surface view of cells supporting a vesicle 1 . 



Throughout their life the vesicles have a well-defined nucleus, 

 and contain a large quantity of protoplasm. When young the 

 protoplasm entirely fills the vesicle (Fig. IV.), but as it increases 

 vacuoles are formed in the protoplasm, so that when the vesicle 

 has obtained its full size a layer of protoplasm lines the inside of 

 the vesicle in close contact with the cell wall, and stands of proto- 

 plasm proceed from this parietal layer to the nucleus (Fig. vi.). 

 The nucleus is generally found in the protoplasm at the base of 

 the vesicle. This protoplasm adheres more firmly to the pitted 

 base of the vesicle, as shewn by the fact that, when the water is 

 absorbed from the vesicle through the action of alcohol the proto- 

 plasm is found generally adhering to the basal wall and in close 

 contact with it (Fig. v.). Where, however, the protoplasm has 

 broken away from this wall it is found elevated and depressed so 

 as accurately to fill the pits. 



As regards the use and function of these vesicles, it would appear 

 probable, from the fact that since the Ice Plant lives in dry sandy 

 places, and that the exterior of the vesicles is protected by being 

 cuticularised, that the vesicles are useful in storing up moisture 

 during times of drought. This proves to be the case, for on an Ice 

 Plant which had been grown in a flower pot with no water given 

 to it, the vesicles became less and less turgid, and finally shrunk 

 up as the soil in the pot became dry ; but when the pot had been 

 copiously watered the vesicles, after a few hours, resumed their 

 former turgidity, and were again subjected to internal pressure. 

 Again the vesicles are always found to be the largest when the 

 plant is well supplied with moisture. If portions of the plant are 

 cut off they remain green, and live for a much longer period than 

 parts of plants which are not provided with reservoirs of moisture ; 

 the vesicles in the meantime become less and less turgid, and 

 shrink. If, however, water is forced into the part at its cut 

 surface the vesicles soon resume their former turgidity and are 

 distended by internal pressure. 



1 Pits at the base of a hair are common, see Sach's Text booh of Botany, 2nd 

 English edition, page 43. 



